1. Field of the Invention
The present invention relates to a display device such as a liquid crystal panel of a personal computer, a TV set and others.
2. Description of the Related Art
Conventionally, there has been a display device such as a liquid crystal panel. (For example, Patent document 1)
As shown in FIG. 13, this display device includes a light guide plate 1, a diffusion film 2, a translucent film 3 (for enhancing a luminance), one surface of which is a substantially flat and another surface has a parallel prismatic shape, a diffusion film 6, and a liquid crystal panel 4, and these are laminated in this order.
Further, other proposals are made for the translucent film having the prismatic shape. (For example, Patent document 2) As shown in FIG. 14, an optical film 60 (equivalent to the above-mentioned translucent film) has a structural surface 64 and a surface 62 opposed to the structural surface 64. The structural surface 64 has a plurality of structures 66 and acts like prisms, however, the heights of the structures 66 vary continuously along their length and the depths of the valleys between the peaks also vary continuously. Moiré (interference fringes) phenomenon of the display device can be prevented by making the peaks and valleys of the prisms to have random shapes with no periodical patterns. Further, a cylindrical mold (roll) used for manufacturing an optical film having the prismatic shape like mentioned above is made by processing a surface of the mold by diamond turning techniques. When processing the mold for the optical film, a pitch of the diamond tool has to be changed randomly so as not to have periodical patterns, for example, the diamond turning tool is put deeply or shallowly at random. However, to change the pitch randomly like this is very difficult.    Patent document 1: JP-A-6-102506 (P. 2, FIG. 3)    Patent document 2: JP-T-2002-504698 (P. 12, FIG. 5)